CBRAM by subtractive etching of metals

ABSTRACT

A method is presented for constructing conductive bridging random access memory (CBRAM) stacks. The method includes forming a plurality of conductive lines within an interlayer dielectric (ILD), forming a CBRAM stack including at least an electrolyte layer, a conductive layer, a metal cap layer, and a top electrode such that a top end of the CBRAM stack has a smaller critical dimension than a bottom end of the CBRAM stack, forming a low-k dielectric layer over the CBRAM stack, and exposing a top surface of the CBRAM stack during a via opening.

BACKGROUND

The present invention relates generally to semiconductor devices, andmore specifically, to a conductive bridging random access memory (CBRAM)constructed by subtractive etching of metals.

CBRAM is considered a promising technology for electronic synapsedevices or memristors for neuromorphic computing as well as high-densityand high-speed non-volatile memory applications. In neuromorphiccomputing applications, a resistive memory device can be employed as aconnection (synapse) between a pre-neuron and post-neuron, representingthe connection weight in the form of device resistance. Multiplepre-neurons and post-neurons can be connected through a crossbar arrayof CBRAMs, which can express a fully-connected neural networkconfiguration.

SUMMARY

In accordance with an embodiment, a method is provided for constructingconductive bridging random access memory (CBRAM) stacks. The methodincludes forming a plurality of conductive lines within an interlayerdielectric (ILD), forming a CBRAM stack including at least anelectrolyte layer, a conductive layer, a metal cap layer, and a topelectrode such that a top end of the CBRAM stack has a smaller criticaldimension than a bottom end of the CBRAM stack, forming a low-kdielectric layer over the CBRAM stack, and exposing a top surface of theCBRAM stack during a via opening.

In accordance with another embodiment, a method is provided forconstructing conductive bridging random access memory (CBRAM) stacks.The method includes forming a plurality of conductive lines within aninterlayer dielectric (ILD), forming a metal nitride layer in directcontact with a conductive line of the plurality of conductive lines, andforming a CBRAM stack including at least an electrolyte layer, aconductive layer, a metal cap layer, and a top electrode such that a topend of the CBRAM stack has a smaller critical dimension than a bottomend of the CBRAM stack.

In accordance with yet another embodiment, a semiconductor device isprovided for constructing conductive bridging random access memory(CBRAM) stacks. The semiconductor device includes a plurality ofconductive lines disposed within an inter-layer dielectric (ILD), abarrier layer disposed in direct contact with a conductive line of theplurality of conductive lines, a bottom electrode disposed over thebarrier layer, an electrolyte layer disposed over the bottom electrode,a conductive layer disposed over the electrolyte layer, a metal caplayer disposed over the conductive layer, a top electrode disposed overthe metal cap layer to define a CBRAM stack, where a top end of theCBRAM stack has a smaller critical dimension than a bottom end of theCBRAM stack, and spacers disposed adjacent the bottom electrode, theelectrolyte layer, the conductive layer, the metal cap layer, and thetop electrode, the spacers extending vertically beyond a top surface ofthe top electrode.

It should be noted that the exemplary embodiments are described withreference to different subject-matters. In particular, some embodimentsare described with reference to method type claims whereas otherembodiments have been described with reference to apparatus type claims.However, a person skilled in the art will gather from the above and thefollowing description that, unless otherwise notified, in addition toany combination of features belonging to one type of subject-matter,also any combination between features relating to differentsubject-matters, in particular, between features of the method typeclaims, and features of the apparatus type claims, is considered as tobe described within this document.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a cross-sectional view of a semiconductor structure includinga plurality of conductive lines formed within a dielectric layer, wherean organic planarization layer (OPL), an anti-reflective coating (ARC)layer, and a photoresist are deposited over the plurality of conductivelines, in accordance with an embodiment of the present invention;

FIG. 2 is a cross-sectional view of the semiconductor structure of FIG.1 where the photoresist is removed, and the OPL and ARC layer are etchedto expose a top surface of one or more of the conductive lines, inaccordance with an embodiment of the present invention;

FIG. 3 is a cross-sectional view of the semiconductor structure of FIG.2 where a metal nitride layer is deposited in a recess of the dielectriclayer and reduced by chemical-mechanical polishing (CMP), in accordancewith an embodiment of the present invention;

FIG. 4 is a cross-sectional view of the semiconductor structure of FIG.3 where a bottom electrode, a hardmask, an organic planarization layer(OPL), an anti-reflective coating (ARC) layer, and a photoresist aredeposited, in accordance with an embodiment of the present invention;

FIG. 5 is a cross-sectional view of the semiconductor structure of FIG.4 where the OPL, the ARC layer, and the photoresist are etched such thata portion of the hardmask remains over the bottom electrode, inaccordance with an embodiment of the present invention;

FIG. 6 is a cross-sectional view of the semiconductor structure of FIG.5 where a conductive bridging random access memory (CBRAM) stack isformed, and then another lithography stack is deposited over the CBRAMstack, in accordance with an embodiment of the present invention;

FIG. 7 is a cross-sectional view of the semiconductor structure of FIG.6 where the OPL is etched, in accordance with an embodiment of thepresent invention;

FIG. 8 is a cross-sectional view of the semiconductor structure of FIG.7 where sacrificial layers are etched to expose a top metal layer, inaccordance with an embodiment of the present invention;

FIG. 9 is a cross-sectional view of the semiconductor structure of FIG.8 where the OPL is stripped, in accordance with an embodiment of thepresent invention;

FIG. 10 is a cross-sectional view of the semiconductor structure of FIG.9 where remaining metal layers are etched to form two CBRAM stacks, inaccordance with an embodiment of the present invention;

FIG. 11 is a cross-sectional view of the semiconductor structure of FIG.10 where a dielectric layer is deposited, in accordance with anembodiment of the present invention;

FIG. 12 is a cross-sectional view of the semiconductor structure of FIG.11 where the dielectric layer is etched to form spacers adjacent the twoCBRAM stacks, in accordance with an embodiment of the present invention;

FIG. 13 is a cross-sectional view of the semiconductor structure of FIG.12 where a top layer of the two CBRAM stacks is partially etched, inaccordance with an embodiment of the present invention;

FIG. 14 is a cross-sectional view of the semiconductor structure of FIG.13 where an interlayer dielectric (ILD) and a plurality of sacrificiallayers are deposited, in accordance with an embodiment of the presentinvention;

FIG. 15 is a cross-sectional view of the semiconductor structure of FIG.14 where the sacrificial layers are etched to form openings directlyover the plurality of conductive lines, in accordance with an embodimentof the present invention;

FIG. 16 is a cross-sectional view of the semiconductor structure of FIG.15 where the CBRAM stack formed over the conductive line is exposed, inaccordance with an embodiment of the present invention; and

FIG. 17 is a cross-sectional view of the semiconductor structure of FIG.16 where a metal fill takes place, the metal fill being planarized, inaccordance with an embodiment of the present invention.

Throughout the drawings, same or similar reference numerals representthe same or similar elements.

DETAILED DESCRIPTION

Embodiments in accordance with the present invention provide methods anddevices for constructing conductive bridging random access memory(CBRAM) devices by a subtractive etching method. The CBRAMs can beemployed for electronic synapse devices or memristors for neuromorphiccomputing as well as high-density and high-speed non-volatile memoryapplications. In neuromorphic computing applications, a resistive memorydevice can be employed as a connection (synapse) between a pre-neuronand post-neuron, representing a connection weight in the form of deviceresistance. Multiple pre-neurons and post-neurons can be connectedthrough a crossbar array of CBRAMs, which can be configured as afully-connected neural network.

CBRAM has a structure in which a solid electrolyte layer is formedbetween top and bottom electrodes, and can have a high current densityby forming a metal bridge inside the solid electrolyte layer. Such aCBRAM is a device exhibiting bidirectional switching behavior, whichmaintains a low resistance state by allowing metal cations to be driftedinto the solid electrolyte layer to form a metal bridge according toapplication of a positive voltage to the top electrode, and maintains ahigh resistance state by allowing a part of the metal bridge to be cutaccording to application of a negative voltage.

Embodiments in accordance with the present invention provide methods anddevices for constructing CBRAM structures between metal lines, whereeach CBRAM structure includes a bottom electrode, an electrolyte layer,a metal layer, a metal cap layer, and a top electrode. Such CBRAMstructures fall under resistive memory technology (RRAM) offeringperformance, power/energy, reliability, and cost advantages overincumbent nonvolatile memory technologies. The CBRAM structures of theexemplary embodiments feature significantly less energy consumption thantoday's leading memories without sacrificing performance andreliability. With a unique combination of fast, low energy operation,the CBRAM structures of the exemplary embodiments are an ideal match forInternet-of-Things (IoT) and other energy-conscious applications.

It is to be understood that the present invention will be described interms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps/blocks can be varied within the scope of the present invention. Itshould be noted that certain features cannot be shown in all figures forthe sake of clarity. This is not intended to be interpreted as alimitation of any particular embodiment, or illustration, or scope ofthe claims.

FIG. 1 is a cross-sectional view of a semiconductor structure includinga plurality of conductive lines formed within a dielectric layer, wherean organic planarization layer (OPL), an anti-reflective coating (ARC)layer, and a photoresist are deposited over the plurality of conductivelines, in accordance with an embodiment of the present invention.

A semiconductor structure 5 includes a plurality of conductive lines 12,14 formed within an inter-layer dielectric (ILD) 10. A dielectric caplayer 16 can be formed over the conductive lines 12, 14. An organicplanarization layer (OPL) or organic dielectric layer (ODL) 18 can thenbe formed over the dielectric cap layer 16. Additionally, ananti-reflective coating (ARC) layer 20 and a photoresist layer 22 can beformed over portions of the OPL 18. Moreover, the structure 5 can bedefined within, e.g., four regions. The first region can designate afirst alignment mark, the second region can designate a second alignmentmark, the third region can designate a periphery region, and the fourthregion can designate a memory region. Alignment marks are used to alignthe wafer such that subsequent layers are formed at the correct locationrelative to underlying features. For example, alignment marks can beused to form the vias and conductive lines in the metallization layersin the correct location to make electrical contact to the devices, suchas transistors, formed in the underlying substrate.

The ILD 10 can include any materials known in the art, such as, forexample, porous silicates, carbon doped oxides, silicon dioxides,silicon nitrides, silicon oxynitrides, or other dielectric materials.The ILD 10 can be formed using any method known in the art, such as, forexample, chemical vapor deposition, plasma enhanced chemical vapordeposition, atomic layer deposition, or physical vapor deposition. TheILD 10 can have a thickness ranging from about 25 nm to about 200 nm.

The dielectric material of layer 10 can include, but is not limited to,ultra-low-k (ULK) materials, such as, for example, porous silicates,carbon doped oxides, silicon dioxides, silicon nitrides, siliconoxynitrides, carbon-doped silicon oxide (SiCOH) and porous variantsthereof, silsesquioxanes, siloxanes, or other dielectric materialshaving, for example, a dielectric constant in the range of about 2 toabout 4.

The metal lines 12, 14 can be formed in the openings or trenches formedin the ILD 10. The metal lines 12, 14 can be any conductive materialsknown in the art, such as, for example, copper (Cu), aluminum (Al), ortungsten (W). The metal lines 12, 14 can be fabricated using anytechnique known in the art, such as, for example, a single or dualdamascene technique. In an embodiment, not illustrated, the metal lines12, 14 can be copper (Cu) and can include a metal liner, where a metalliner can be metals, such as, for example, tantalum nitride and tantalum(TaN/Ta), titanium, titanium nitride, cobalt, ruthenium, and manganese.

The dielectric cap layer 16 can be referred to as a barrier layer. Thedielectric material of the dielectric cap layer 16 can be siliconnitride (SiN).

The OPL 18 and the ARC layer 20 can be employed as a lithographic stackto pattern the underlying layers. The OPL 18 can be formed at apredetermined thickness to provide reflectivity and topography controlduring etching of the hard mask layers below. The OPL 18 can include anorganic material, such as a polymer. The thickness of the OPL 18 can bein a range from about 50 nm to about 300 nm. In one example, thethickness of the OPL 18 is about 135 nm.

The layer 20 is an ARC layer which minimizes the light reflection duringlithography for a lithography stack. The ARC layer 20 can includesilicon, for example, a silicon anti-reflective layer (SiARC). Thethickness of the ARC layer 20 can be in range from about 10 nm to about100 nm. The anti-reflective film layer 20 can be an antireflective layerfor suppressing unintended light reflection during photolithography.Exemplary materials for an antireflective layer include, but are notlimited to, metal silicon nitrides, or a polymer film. Theanti-reflective layer can be formed, depending on materials, forexample, using sputter deposition, chemical vapor deposition, or spincoating.

A photolithography process usually includes applying a layer ofphotoresist material 22 (e.g., a material that will react when exposedto light), and then selectively exposing portions of the photoresist 22to light or other ionizing radiation (e.g., ultraviolet, electron beams,X-rays, etc.), thereby changing the solubility of portions of thematerial. The resist 22 is then developed by washing the resist with adeveloper solution, such as, e.g., tetramethylammonium hydroxide (TMAH),thereby removing non-irradiated (in a negative resist) or irradiated (ina positive resist) portions of the resist layer.

FIG. 2 is a cross-sectional view of the semiconductor structure of FIG.1 where the photoresist is removed, and the OPL and ARC layer are etchedto expose a top surface of one or more of the conductive lines, inaccordance with an embodiment of the present invention.

In various example embodiments, the OPL 18, the ARC layer 20, and thephotoresist 22 are etched to form an opening or trench 26 to expose atop surface 11 of the ILD 10 and to form an opening or trench 28 toexpose a top surface 15 of conductive line 14. Additionally, a topsurface 17 of the dielectric cap layer 16 is exposed.

FIG. 3 is a cross-sectional view of the semiconductor structure of FIG.2 where a metal nitride layer is deposited in a recess of the dielectriclayer and reduced by chemical-mechanical polishing (CMP), in accordancewith an embodiment of the present invention.

In various example embodiments, a metal nitride liner is deposited andthen recessed by, e.g., CMP such that a first metal nitride layer 30 isformed in the trench 26 and a second metal nitride layer 32 is formed inthe trench 28 and over the conductive line 14. The first and secondmetal nitride layers 30, 32 are planarized by, e.g., CMP, such that topsurfaces of the first and second metal nitride layers 30, 32 are flushwith a top surface 17 of the dielectric cap layer 16. In a preferredembodiment, the first and second metal nitride layers 30, 32 aretantalum nitride (TaN) layers. The metal nitride layers 30, 32 can bereferred to as barrier layers.

FIG. 4 is a cross-sectional view of the semiconductor structure of FIG.3 where a bottom electrode, a hardmask, an organic planarization layer(OPL), an anti-reflective coating (ARC) layer, and a photoresist aredeposited, in accordance with an embodiment of the present invention.

In various example embodiments, a bottom electrode 34 is deposited. Thebottom electrode 34 is in direct contact with the first and second metalnitride layers 30, 32. Then a hardmask 36 is deposited over the bottomelectrode 34.

The bottom electrode 34 can include a conductive material, such as Cu,Al, Ag, Au, Pt, W, etc. In some embodiments, the bottom electrode 34 caninclude nitrides such as TiN, TaN, Ta or Ru. In a preferred embodiment,the bottom electrode 34 is TiN.

In various example embodiments, the hardmask layer 36 can be a nitride,for example, a silicon nitride (SiN), an oxynitride, for example,silicon oxynitride (SiON), or a combination thereof. In a preferredembodiment, the hardmask layer 36 can be silicon nitride (SiN), forexample, Si₃N₄.

In one or more embodiments, the hardmask layer 36 can have a thicknessin the range of about 20 nm to about 100 nm, or in the range of about 35nm to about 75 nm, or in the range of about 45 nm to about 55 nm,although other thicknesses are contemplated.

Subsequently, an organic planarization layer (OPL) or organic dielectriclayer (ODL) 38 can then be formed over the hardmask layer 36.Additionally, an anti-reflective coating (ARC) layer 40 and aphotoresist layer 42 can be formed over portions of the OPL 38. Thethickness of the OPL 38 can be in a range from about 50 nm to about 300nm. In one example, the thickness of the OPL 38 is about 100 nm.

FIG. 5 is a cross-sectional view of the semiconductor structure of FIG.4 where the OPL, the ARC layer, and the photoresist are etched such thata portion of the hardmask remains over the bottom electrode, inaccordance with an embodiment of the present invention.

In various example embodiments, the OPL 38, the ARC layer 40, and thephotoresist 42 are etched to form a hardmask portion 44 over the bottomelectrode 34. Additionally, a top surface 35 of the bottom electrode 34is exposed. The hardmask portion 44 is offset from the conductive lines12, 14. The hardmask portion 44 is offset from the first and secondmetal nitride layers 30, 32.

FIG. 6 is a cross-sectional view of the semiconductor structure of FIG.5 where a conductive bridging random access memory (CBRAM) stack isformed, and then another lithography stack is deposited over the CBRAMstack, in accordance with an embodiment of the present invention.

In various example embodiments, the CBRAM stack is formed and includes afirst layer 50, a second layer 52, a third layer 54, a fourth layer 56,and a fifth layer 58. The first layer 50 can be an electrolyte layer,e.g., a silicon monoxide (SiO) hardmask layer, the second layer 52 canbe a conductive layer, e.g., a copper (Cu) layer, the third layer 54 canbe a metal cap layer, e.g., a ruthenium (Ru) layer, the fourth layer 56can be, e.g., a tantalum nitride (TaN) layer, and the fifth layer 58 canbe, e.g., hardmask layer, such as a SiO and a SiN hardmask layer. Thesecond, third, and fourth layers 52, 54, 56 can be referred to as metallayers. At least one of these layers can be formed from a thermallystable metal, such as TiN, TaN, TaC, TiAlN, TaAlN, or their derivatives.

In various embodiments, a lithographic stack can be formed over theCBRAM stack. The lithographic stack can include an organic planarizationlayer (OPL) or organic dielectric layer (ODL) 60 that can be formed overthe hardmask layer 58 of the CBRAM stack. Additionally, ananti-reflective coating (ARC) layer 62 and a photoresist layer 64 can beformed over portions of the OPL 60. The thickness of the OPL 60 can bein a range from about 50 nm to about 300 nm. In one example, thethickness of the OPL 60 is about 200 nm.

FIG. 7 is a cross-sectional view of the semiconductor structure of FIG.6 where the OPL is etched, in accordance with an embodiment of thepresent invention.

In various example embodiments, the OPL 60 is etched to form OPL regions60′. Additionally, ARC layers 62′ remain over the OPL regions 60′. A topsurface 59 of the hardmask layer 58 is also exposed.

FIG. 8 is a cross-sectional view of the semiconductor structure of FIG.7 where sacrificial layers are etched to expose a top metal layer, inaccordance with an embodiment of the present invention.

In various example embodiments, the fourth layer 56 (TaN layer) and thefifth layer 58 (SiO) layer are removed by etching, e.g., dry etching. Atop surface 55 of the third layer 54 (Cu layer) is now exposed.Additionally, CBRAM stacks are beginning to take shape as a first layer72 and a second layer 70 are formed under the first OPL region 60′ for afirst CBRAM structure and a first layer 82 and a second layer 80 areformed under the second OPL region 60′ for the second CBRAM structure.The first and second layers 72, 70 are aligned with the metal nitridelayer 30 and the first and second layers 82, 80 are aligned with themetal nitride layer 32.

The dry etching process can implement fluorine-containing gas (e.g.,CF₄, SF₆, CH₂F₂, CHF₃, and/or C₂F₆), chlorine-containing gas (e.g., Cl₂,CHCl₃, CCl₄, and/or BCl₃), bromine-containing gas (e.g., HBr and/orCHBR₃), oxygen-containing gas, iodine-containing gas, other suitablegases and/or plasmas, or combinations thereof. The etching process caninclude a multiple-step etching to gain etch selectivity, flexibilityand desired etch profile.

FIG. 9 is a cross-sectional view of the semiconductor structure of FIG.8 where the OPL is stripped, in accordance with an embodiment of thepresent invention.

In various example embodiments, the OPL regions 60′ are etched to exposea top surface 71 of the first CBRAM structure and a top surface 81 ofthe second CBRAM structure. Plasma etching can be used to etch the OPLregions 60′.

FIG. 10 is a cross-sectional view of the semiconductor structure of FIG.9 where remaining metal layers are etched to form two CBRAM stacks, inaccordance with an embodiment of the present invention.

In various example embodiments, the first, second, and third layers 50,52, 54 are etched to form the CBRAM stacks 75, 85. A top surface 35 ofthe bottom electrode 34 is also exposed.

The first CBRAM stack 75 includes 5 layers. The first layer 72 can be aTaN layer, the second layer 74 can be a ruthenium (Ru) layer, the thirdlayer 76 can be a copper (Cu) layer, and the fourth layer 78 can be asilicon monoxide (SiO) layer. The fourth layer 78 is formed over thebottom electrode 34 that completes the CBRAM stack 75. In one exampleembodiment, the bottom electrode 34 can be optional.

Similarly, the second CBRAM stack 85 includes 4 layers. The first layer82 can be a TaN layer, the second layer 84 can be a ruthenium (Ru)layer, the third layer 86 can be a copper (Cu) layer, and the fourthlayer 88 can be a silicon monoxide (SiO) layer. The fourth layer 88 isformed over the bottom electrode 34 that completes the CBRAM stack 85.In one example embodiment, the bottom electrode 34 can be optional.

Therefore, the CBRAM stacks 75, 85 are built between metal lines 12, 14,the CBRAM bottom electrode 34 can be, e.g., TiN, TaN, or W and the CBRAMtop electrode can be, e.g., Ti, TiN, Ta, TaN or W.

FIG. 11 is a cross-sectional view of the semiconductor structure of FIG.10 where a dielectric layer is deposited, in accordance with anembodiment of the present invention.

In various example embodiments, a SiN encapsulation 90 takes place. TheSiN layer 90 encapsulates both the first and second CBRAM stacks 75, 85.

FIG. 12 is a cross-sectional view of the semiconductor structure of FIG.11 where the dielectric layer is etched to form spacers adjacent the twoCBRAM stacks, in accordance with an embodiment of the present invention.

In various example embodiments, the SiN layer 90 is etched to formspacers 92 adjacent the first CBRAM stack 75, spacers 94 adjacent thesecond CBRAM stack 85, and spacers 96 adjacent the SiN hardmask portion44. The SiN layer 90 can be selectively etched by, e.g., RIE. The etchalso results in the exposure of the top surfaces of the layers 72, 82 ofthe first and second CBRAM stacks 75, 85, respectively.

FIG. 13 is a cross-sectional view of the semiconductor structure of FIG.12 where a top layer of the two CBRAM stacks is partially etched, inaccordance with an embodiment of the present invention.

In various example embodiments, the layers 72, 82 are partially etchedsuch that the first CBRAM stack 75 includes a remaining first layer 72′and the second CBRAM stack 85 includes a remaining first layer 82′. Arecess or gap region 91 is formed between the spacers 92 of the firstCBRAM stack 75 and a recess or gap region 93 is formed between thespacers 94 of the second CBRAM stack 85. Additionally, the bottomelectrode is etched such that bottom electrode portions 34′ remain.

FIG. 14 is a cross-sectional view of the semiconductor structure of FIG.13 where an interlayer dielectric (ILD) and a plurality of sacrificiallayers are deposited, in accordance with an embodiment of the presentinvention.

In various example embodiments, a SiN encapsulation 100 takes place. TheSiN encapsulation 100 fills the gap region 91 of the first CBRAM stack75 and the gap region 92 of the second CBRAM stack 85. The SiNencapsulation 100 encapsulates or encompasses or envelopes the first andsecond CBRAM stacks 75, 85.

In various example embodiments, a low-k dielectric layer 102 is thendeposited over the SiN encapsulation 100. A low-k dielectric material asused in the low-k dielectric layer 102 can have a dielectric constantthat is less than 4.0, e.g., 3.9. In one embodiment, the low-k materiallayer 102 can have a dielectric constant ranging from about 1.0 to about3.5. In another embodiment, the low-k material layer 102 can have adielectric constant ranging from about 1.75 to about 3.2.

One example of a material suitable for the low-k materials for the low-kdielectric layer 102 can include silicon oxycarbonitride (SiOCN). Otherlow-k materials that can also be used for the low-k dielectric layer 102can include fluorine doped silicon dioxide, carbon doped silicondioxide, porous silicon dioxide, porous carbon doped silicon dioxide,organosilicate glass (OSG), diamond-like carbon (DLC) and combinationsthereof.

In some example embodiments, the low-k dielectric layer 102 can beconformally deposited using chemical vapor deposition (CVD). Variationsof CVD processes suitable for forming the first dielectric layerinclude, but are not limited to, Atmospheric Pressure CVD (APCVD), LowPressure CVD (LPCVD) and Plasma Enhanced CVD (PECVD), Metal-Organic CVD(MOCVD) and combinations thereof can also be employed. In someembodiments, the low-k dielectric layer 102 can have a thickness rangingfrom about 5 nm to about 30 nm. In another embodiment, the low-kdielectric layer 102 can have a thickness ranging from about 7 nm toabout 15 nm.

Subsequently, a plurality of sacrificial layers can be deposited. In oneexample, a first sacrificial layer 104, a second sacrificial layer 106,and a third sacrificial layer 108 are deposited over the low-kdielectric layer 102. In one example, the first sacrificial layer 104can be a SiN layer, the second sacrificial layer 106 can be a TiNhardmask, and the third sacrificial layer 108 can be a TEOS hard mask(tetraethyl orthosilicate, Si(OC₂H₅)₄).

FIG. 15 is a cross-sectional view of the semiconductor structure of FIG.14 where the sacrificial layers are etched to form openings directlyover the plurality of conductive lines, in accordance with an embodimentof the present invention.

In various example embodiments, the second and third sacrificial layers106, 108 can be etched by, e.g., RIE, to create a first opening orrecess 110 over the conductive line 12 and to create a second opening orrecess 110 over the conductive line 14. The first sacrificial layer 104is not removed. The top surface of the first sacrificial layer 104remains intact in the first and second openings 110. The thirdsacrificial layer 108 is completely removed such that a top surface ofthe second sacrificial layer 106 is exposed in areas where the openings110 do not occur.

FIG. 16 is a cross-sectional view of the semiconductor structure of FIG.15 where the CBRAM stack formed over the conductive line is exposed, inaccordance with an embodiment of the present invention.

In various example embodiments, vias are formed. A first via 120 extendsto a top surface 13 of the conductive line 12 and a second via 122extends to a top surface 81 of the layer 82′. Additionally, spacers 94are maintained. The CBRAM structure includes the bottom electrodeportion 34′, the electrolyte layer 78, the conductive layer 76 (e.g.,Cu), the metal cap layer 74 (e.g., Ru), and the top electrode 72 (e.g.,TaN).

In a conventional damascene process, the Cu pillars with the smallercritical dimension (CD) are at the bottom end. In contrast, in theexemplary embodiments of the present invention, by employing subtractivepatterning, the CBRAM stack has a smaller CD at the top end of the CBRAMpillar and a larger CD at the bottom end of the CBRAM pillar. Therefore,a top end of the CBRAM stack has a smaller critical dimension than thebottom end of the CBRAM stack.

In various embodiments, the first and second sacrificial layers 104, 106are also completely removed to expose a top surface 101 of the low-kdielectric layer 102.

FIG. 17 is a cross-sectional view of the semiconductor structure of FIG.16 where a metal fill takes place, the metal fill being planarized, inaccordance with an embodiment of the present invention.

In various example embodiments, a conductive material 130 can bedeposited. The metallization can be a single damascene metallization.Thus, only single damascene metallization is needed for the trench, thusenabling dynamic reflow or other fill techniques that are sensitive topattern and profile needs. The conductive material 130 can be metalsinclude copper (Cu), cobalt (Co), aluminum (Al), platinum (Pt), gold(Au), tungsten (W), titanium (Ti), or any combination thereof. The metalcan be deposited by a suitable deposition process, for example, chemicalvapor deposition (CVD), plasma enhanced chemical vapor deposition(PECVD), physical vapor deposition (PVD), plating, thermal or e-beamevaporation, or sputtering.

In various exemplary embodiments, the height of the conductive material130 can be reduced by chemical-mechanical polishing (CMP) and/oretching. Therefore, the planarization process can be provided by CMP.Other planarization process can include grinding and polishing.

In various example embodiments, the bottom electrode 34 or bottomelectrode portions 34′ can be optional. In other words, the SiO layercan directly contact the second metal nitride layer 32.

As used throughout the instant application, the term “copper” isintended to include substantially pure elemental copper, copperincluding unavoidable impurities including a native oxide, and copperalloys including one or more additional elements such as carbon,nitrogen, magnesium, aluminum, titanium, vanadium, chromium, manganese,nickel, zinc, germanium, strontium, zirconium, silver, indium, tin,tantalum, and platinum. In embodiments, the copper alloy is acopper-manganese alloy. In further embodiments, in lieu of copper,cobalt metal (Co) or cobalt metal alloys can be employed. Thecopper-containing structures are electrically conductive. “Electricallyconductive” as used through the present disclosure refers to a materialhaving a room temperature conductivity of at least 10⁻⁸ (Ω-m)⁻¹.

In conclusion, a structure for a CBRAM is built or constructed by asubtractive etching method. The CBRAM stacks are built between Cu lines.The CBRAM bottom electrode can be, e.g., TiN, TaN, or W. The CBRAMelectrolyte can be, e.g., SiO, a-Si. The CBRAM conductive element canbe, e.g., Cu, Ag. The CBRAM metal cap on the conductive element can be,e.g., Ru, Ir, Pt. The CBRAM top electrode can be, e.g., Ti, TiN, Ta,TaN, or W and combination thereof. The CBRAM encapsulation or spacer canbe, e.g., SiN. The bottom electrode, the electrolyte layer, theconductive layer, the metal cap layer, and the top electrode cancollectively form the CBRAM structure.

It is to be understood that the present invention will be described interms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps/blocks can be varied within the scope of the present invention.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements can also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements can be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

The present embodiments can include a design for an integrated circuitchip, which can be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer can transmit the resulting designby physical mechanisms (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which include multiple copies of the chipdesign in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer to beetched or otherwise processed.

Methods as described herein can be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It should also be understood that material compounds will be describedin terms of listed elements, e.g., SiGe. These compounds includedifferent proportions of the elements within the compound, e.g., SiGeincludes Si_(x)Ge_(1-x) where x is less than or equal to 1, etc. Inaddition, other elements can be included in the compound and stillfunction in accordance with the present embodiments. The compounds withadditional elements will be referred to herein as alloys. Reference inthe specification to “one embodiment” or “an embodiment” of the presentinvention, as well as other variations thereof, means that a particularfeature, structure, characteristic, and so forth described in connectionwith the embodiment is included in at least one embodiment of thepresent invention. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This can be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” when usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, can be used herein for ease of description todescribe one element's or feature's relationship to another element(s)or feature(s) as illustrated in the FIGS. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the FIGS. For example, if the device in theFIGS. is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device can be otherwise oriented (rotated 90degrees or at other orientations), and the spatially relativedescriptors used herein can be interpreted accordingly. In addition, itwill also be understood that when a layer is referred to as being“between” two layers, it can be the only layer between the two layers,or one or more intervening layers can also be present.

It will be understood that, although the terms first, second, etc. canbe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another element. Thus, a first element discussed belowcould be termed a second element without departing from the scope of thepresent concept.

Having described preferred embodiments of a method for constructing aCBRAM with subtractive methods (which are intended to be illustrativeand not limiting), it is noted that modifications and variations can bemade by persons skilled in the art in light of the above teachings. Itis therefore to be understood that changes may be made in the particularembodiments described which are within the scope of the invention asoutlined by the appended claims. Having thus described aspects of theinvention, with the details and particularity required by the patentlaws, what is claimed and desired protected by Letters Patent is setforth in the appended claims.

The invention claimed is:
 1. A method for constructing conductivebridging random access memory (CBRAM) stacks, the method comprising:forming a plurality of conductive lines within an interlayer dielectric(ILD); forming a CBRAM stack including at least an electrolyte layer, aconductive layer, a metal cap layer, and a top electrode such that a topend of the CBRAM stack has a smaller critical dimension than a bottomend of the CBRAM stack; forming a low-k dielectric layer over the CBRAMstack; and exposing a top surface of the CBRAM stack during a viaopening.
 2. The method of claim 1, further comprising forming a barrierlayer over a conductive line of the plurality of conductive lines inalignment with the CBRAM stack.
 3. The method of claim 2, furthercomprising forming an encapsulation layer over the CBRAM stack.
 4. Themethod of claim 3, further comprising etching the encapsulation layer toform spacers adjacent the CBRAM stack.
 5. The method of claim 4, furthercomprising selectively recessing the plurality of sacrificial layers tocreate an opening in alignment with the CBRAM stack.
 6. The method ofclaim 5, wherein the plurality of sacrificial layers includes a firstsacrificial layer, a second sacrificial layer, and a third sacrificiallayer.
 7. The method of claim 1, further comprising filling the viaopening with a conductive material.
 8. The method of claim 1, whereinthe electrolyte layer is a silicon monoxide (SiO) layer, the conductivelayer includes copper (Cu), and the metal cap layer includes ruthenium(Ru).
 9. The method of claim 1, wherein the CBRAM stack further includesa bottom electrode.
 10. A method for constructing conductive bridgingrandom access memory (CBRAM) stacks, the method comprising: forming aplurality of conductive lines within an interlayer dielectric (ILD);forming a metal nitride layer in direct contact with a conductive lineof the plurality of conductive lines; and forming a CBRAM stackincluding at least an electrolyte layer, a conductive layer, a metal caplayer, and a top electrode such that a top end of the CBRAM stack has asmaller critical dimension than a bottom end of the CBRAM stack.
 11. Themethod of claim 10, wherein the CBRAM stack further includes a bottomelectrode, the bottom electrode in direct contact with the metal nitridelayer.
 12. The method of claim 11, further comprising forming anencapsulation layer over the CBRAM stack.
 13. The method of claim 12,further comprising etching the encapsulation layer to form spacersadjacent the CBRAM stack.
 14. The method of claim 13, further comprisingselectively recessing the plurality of sacrificial layers to create anopening in alignment with the CBRAM stack.
 15. The method of claim 14,wherein the plurality of sacrificial layers includes a first sacrificiallayer, a second sacrificial layer, and a third sacrificial layer. 16.The method of claim 10, further comprising forming a low-k dielectriclayer over the CBRAM stack and exposing a top surface of the CBRAM stackduring a via opening.
 17. The method of claim 16, further comprisingfilling the via opening with a conductive material.
 18. The method ofclaim 10, wherein the electrolyte layer is a silicon monoxide (SiO)layer, the conductive layer includes copper (Cu), and the metal caplayer includes ruthenium (Ru).